In recent years, higher integration of a semiconductor device, a decrease in a mounting area, and a decrease in wiring resistance due to a decrease in the distance between wirings have been required with higher performance and miniaturization of an electronic appliance such as a cell phone and an IC card. As a procedure for the requirement, a laminated structure in which semiconductor elements are stacked longitudinally has been investigated.
An example of a method for producing a stack structure includes the following process. In the process, a wafer with a semiconductor element is bonded to a supporting substrate using a temporary adhesive or the like, a back surface of the wafer is made thin, a through hole is formed by a through silicon via (TSV) technology using a technique such as anisotropic dry etching, the through hole is filled with a conductive material such as copper to form an electrode on the back surface, an insulating film is formed on the back surface of the wafer with the electrode, and a chip or a wafer with another semiconductor element is electrically bonded to the insulating film.
In the process, the insulating film formed on the back surface of the wafer is required to have properties such as electrical insulation properties of preventing current leakage between electrodes, migration of a conductive material, and the like, solvent resistance at a photolithography step after forming an insulating film, and heat resistance at an electrode bonding step, and to express the properties at lower baking temperature from the viewpoint of heat resistance of a member.
Examples of a publicly known insulating film include insulating films formed by spin coating such as a polyimide, a polybenzoxazole, and an aromatic polyether. However, a polyimide and a polybenzoxazole have problems in which good insulating properties and solvent resistance are not obtained at a baking temperature of about 180° C., and a reaction of an unreacted moiety is further promoted at a heating step after formation, to shrink the insulating film.
An aromatic polyether has problems in which the solvent resistance is low due to the absence of thermal cross-linking moiety and a resin is molten by electrode bonding due to the low softening point of the resin.
A passivation film containing a polymer, such as a polyether and a polyetherether ketone, having an organic group including a double bond and a triple bond at a terminal or a side chain of the polymer has been disclosed (see Patent Document 1). However, an aromatic polyether described in Patent Document 1 does not have sufficient properties at 180° C. Further, there is a problem in which electrical insulation properties are deteriorated at a high temperature process.
A resin composition containing a polyether compound and a benzoxazine compound using a crosslinker has been disclosed (see Patent Document 2). As the crosslinker, an isocyanate has been disclosed.